The present invention relates to an electric heating device for heating air, which is especially suitable for use as a supplementary electric heating in motor vehicles.
In motor vehicles heating devices or radiators are used for heating the vehicle interior and/or the engine. On the one hand, they are used when the engine is started, as long as the engine does not yet provide sufficient heat energy. On the other hand, especially consumption-optimized internal combustion engines make it necessary to use such heating devices in motor vehicles.
The use of such heating devices is, however, not restricted to the field of automotive vehicles. These heating devices are also suitable to be used for a great variety of other purposes, e.g. in the field of domestic installations (room air conditioning), industrial plants and the like.
EP-A2-0 901 311 discloses an electric heating means for motor vehicles. The heating device described comprises a plurality of heating elements which are combined so as to form a heating block. The heating block and a control device for controlling the heating elements are held in a common frame. In this way, the control device defines a structural unit together with the heating block held in the frame. The control device comprises a power electronics with electronic switches which are provided with cooling bodies. The control device is arranged in such a way that the main part of an air current to be heated flows through the heating block and that a boundary portion of said air current is applied to the control device for the purpose of cooling.
This known heating device is disadvantageous insofar as the air current flowing over the control device reduces the total effectiveness of the heating power. The part of the air current to be heated which passed the heating block and the part which flowed past the control device have different output temperatures. The output temperature of the air current which was applied to the control device is markedly lower than that of the main current. This results especially in an inhomogeneous air discharge temperature. In addition, the heating device will be less effective when air having a lower temperature flows in.
It is therefore the object of the present invention to provide an electric heating device by means of which more effective heating can be achieved.
This object is achieved by the features of claim 1.
According to the present invention, the air to be heated is not applied to the control device as a whole, but the amount of air passing through and used for cooling the power electronics can be controlled through window openings. In this way, an adaptation to the amount of air passing through the heating block is possible so that both amounts of air will have substantially the same output temperature. In this way, the effectiveness of the whole heating device will not be reduced by an air current which is diverted for cooling the control electronics.
According to an advantageous embodiment of the present invention, means for influencing the air current are provided within the area between opposed window openings. In this way, the air current can be conducted such that it is optimally applied to the cooling elements of the power electronics so that the maximum possible heating of the cooling air current will be achieved. A particularly advantageous variant can be accomplished by means of U-shaped cooling elements in the case of which additional air-conducting elements can be provided which project between the legs of the U-shaped cooling elements.
The cooling air can be heated still further, when it is also conducted over the components of the control device. For this purpose, the printed circuit board of the control device is preferably equipped with components on only one side thereof. A particularly simple application of air to the components can be achieved in this way. In addition, such an arrangement of the components is also particularly advantageous for reasons of production engineering.
In accordance with an advantageous embodiment of the present invention, the printed circuit board is arranged at right angles to the plane of the frame. This kind of arrangement permits, on the one hand, a simple application of air to the components. On the other hand, a small construction depth of the electric heating device can be achieved in this way.
The control device can be fixed in a particularly simple manner when the electric connection lugs of the heating elements, which project into the box of the lateral bar, are used for such fixing. For this purpose, spring elements which are complementary to the connection lugs can be provided on the printed circuit board. This embodiment permits, with the aid of the same means, electric contacting, e.g. for conducting the control currents for the heating elements, as well as mechanical fixing. This has the effect that the amount of material required. for an electric heating device according to the present invention and the investment in the production process of such an electric heating device will be reduced substantially.
Further advantageous embodiments of the present invention are disclosed in the subclaims.